Gold Phosphole Complexes as Efficient Catalysts for Alkyne Activation

Abstract

Gold(I) complexes bearing monophosphole ligands were synthesized, and their electronic and steric properties were compared to those of their triphenylphosphine-based counterparts. Cationic phosphole-based gold(I) complexes are active and selective in enyne cycloisomerization and in olefin cyclopropanation, with a good correlation between the ligand σ-donor ability and the catalytic activity. For the most efficient ligand, 1-phenyl-2,3,4,5-tetramethylphosphole (TMP), a highly active, selective, and stable cationic [Au(TMP)(CH 3 CN)]SbF 6 complex was isolated.

Platinum(ii)–phosphole complexes: synthesis and evaluation as enyne cycloisomerisation catalysts

“…The relative position of the phosphole ligands in the platinum complexes was easily determined by measuring the magnitude of 1 J P-Pt in the 195 Pt isotopomer in 31 P NMR spectroscopy. Notably the same trend was observed in the determination of 1 J ( 77 Se, 31 P) in the corresponding phosphole-selenides, 16 indicating that TMP is the best σ-donor ligand of the series. 17a-f Moreover, as depicted in Table 1, both the phosphorus-platinum coupling constant, 1 J ( 195 Pt, 31 P), and the coordination chemical shift, Δδ( 31 P), increase in the order TMP < DMP < DBP.…”

“…Notably the same trend was observed in the determination of 1 J ( 77 Se, 31 P) in the corresponding phosphole-selenides, 16 indicating that TMP is the best σ-donor ligand of the series. 16 Geometrical parameters within the P-Pt-P backbone in three cis-[Pt(L) 2 Cl 2 ] phosphole complexes are summarized in Table 2. 16 On the other hand, [Pt(TPP) 2 Cl 2 ] exhibited the two phosphole ligands in the trans position as indicated by a 1 J ( 195 Pt, 31 P) coupling constant of 2520 Hz (Table 1, entry 4).…”

“…7 Various nucleophiles have been used in such reactions, including water or alcohols, 8 to promote hydroxy-or alcoxycyclisations or electron-rich arenes such as indole 8g,9 to promote hydroarylation-cyclisation tandem reactions. 5,13 Given the various applications of phosphole-based ligands in homogeneous catalysis 15 and following our previous report on gold(I) phosphole complexes, which are both active and selective in enyne cycloisomerisation, 16 we report herein the synthesis of a series of new platinum(II) monophosphole complexes and their evaluation in 1,6-enyne cycloisomerisations and related reactions. Then the role of ligands in Pt(II)-complexes on the activity and/or the selectivity was demonstrated.…”

“…17a-f Moreover, as depicted in Table 1, both the phosphorus-platinum coupling constant, 1 J ( 195 Pt, 31 P), and the coordination chemical shift, Δδ( 31 P), increase in the order TMP < DMP < DBP. 16 On the other hand, [Pt(TPP) 2 Cl 2 ] exhibited the two phosphole ligands in the trans position as indicated by a 1 J ( 195 Pt, 31 P) coupling constant of 2520 Hz (Table 1, entry 4). By comparison, the analogous cis-[Pt(PPh 3 ) 2 Cl 2 ] complex shows a larger 1 J ( 195 Pt, 31 P) coupling constant (3681 Hz) and a larger Δδ( 31 P) (20.3 ppm), 22 which highlights a specific behaviour of phosphole ligands towards platinum coordination that may lead to specific activities of phosphole-based complexes in catalysis as already observed in gold catalysis.…”

“…With the DBP-based complex, the cycloisomerisation of 1a is slower but more selective in cyclopropane 2a (Table 3, entry 5), which can be attributed to the higher steric hindrance of DBP versus TMP. 16 Following this preliminary screening, cis-[Pt(TMP) 2 Cl 2 ] was selected as the preferred catalytic precursor and a second series of experiments was performed in order to determine the optimal experimental conditions. TMP thus appeared as the best ligand of the series in terms of activity in the cycloisomerisation of 1a, as already observed in Au-catalysed cycloisomerisation.…”